The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a capacitor using a metal layer, e.g., a ruthenium (Ru) layer, as a lower electrode or an upper electrode in a semiconductor device.
Generally, a capacitor in a memory cell includes a lower electrode for a storage, a dielectric layer, and an upper electrode for a plate. To acquire a large capacitance within limited dimensions, it is required to secure a thin dielectric layer, decrease effective dimensions by forming a three-dimensional capacitor, or apply a dielectric layer with a high permittivity such as a tantalum pentoxide (Ta2O5) layer.
When the Ta2O5 layer is used as a dielectric layer in a capacitor having a structure of Metal-Insulator-Polysilicon (MIS) where a lower electrode includes polysilicon, the polysilicon is oxidized during a high temperature heat treatment process performed after the formation of the Ta2O5 layer. Thus, a valid dielectric layer becomes thick decreasing the capacitor capacitance. Furthermore, it is difficult to acquire precise electric characteristics from the capacitor due to an electric current change caused by an asymmetrical electric current-voltage characteristic of the MIS-structured capacitor.
Thus, for instance, when the capacitor is formed to have a thickness not greater than 0.1 μm, it employs a structure having the metal layer, e.g., a Ru layer, as a lower electrode, instead of polysilicon, such as a Metal-Insulator-Metal (MIM) structure or the MIP structure. For instance, in the MIM-structured capacitor, a metal layer for a lower electrode, a dielectric layer, and a metal layer for an upper electrode are sequentially formed over a substrate obtained through a certain process. Herein, the metal layer for a lower electrode and metal layer for an upper electrode may be the Ru layer with a low resistivity. The Ru layer is formed through an Atomic Layer Deposition (ALD) process because of a structural characteristic of the MIM capacitor.
However, when the Ru layer is formed through the ALD process, an adhesive strength is not good even though the adhesive strength changes according to the substrate material which is an adhesion target. Thus, the Ru layer swells up in a blister shape (i.e., lose adhesion and delaminates). This result makes it hard to fabricate the capacitor and deteriorates the characteristics, e.g., capacitance and leakage current. A technology needs to be developed for increasing the adhesive strength of the Ru layer during the fabrication of the capacitor using the Ru layer with a low resistivity as a lower electrode or an upper electrode.